Re: checking for a NULL date in a partitioned table kills performance

Hi Sbob,
Have you tried using the following indexes ?

B-tree

-

The default and most commonly used type, ideal for equality, range
and Pattern queries.

BRIN (Block Range INdex)

-

Compact indexes that are efficient for large tables where the data is
naturally ordered.

On Fri, 23 Aug 2024 at 02:45, Sbob <sbob(at)quadratum-braccas(dot)com> wrote:

> All;
>
> I am running a select from a partitioned table. The table (and all the
> partitions) have an index on contract_date like this:
> CREATE INDEX on part_tab (contract_date) where contract_date >
> '2022-01-01'::date
>
> The table (including all partitions) has 32million rows
> The db server is an aurora postgresql instance with 128GB of ram and 16
> vcpu's
>
> The shared buffers is set to 90GB and effective_cache_size is also 90GB
> I set default_statistics_target to 1000 and ram a vacuum analyze on the
> table
>
> I am selecting a number of columns and specifying this where clause:
>
> WHERE (
> (contract_date IS NULL)
> OR
> (contract_date > '2022-01-01'::date)
> )
>
> This takes 15 seconds to run and an explain says it's doing a table scan
> on all partitions (the query is not specifying the partition key)
> If I change the where clause to look like this:
>
> WHERE (
> (contract_date > '2022-01-01'::date)
> )
>
> Then it performs index scans on all the partitions and runs in about 600ms
>
> If i leave the where clause off entirely it performs table scans of the
> partitions and takes approx 18 seconds to run
>
> I am trying to get the performance to less than 2sec,
> I have tried adding indexes on the table and all partitions like this:
> CREATE INDEX ON table (contract_date NULLS FIRST) ;
> but the performance with the full where clause is the same:
>
> WHERE (
> (contract_date IS NULL)
> OR
> (contract_date > '2022-01-01'::date)
> )
>
> runs in 15 seconds and scans all partitions
>
> I also tried indexes i=on the table and all partitions like this:
> CREATE INDEX ON table (contract_date) WHERE contract_date IS NULL;
>
> but I get the same result, table scans on all partitions and it runs in
> 15 seconds
>
> Any help or advice ?
>
> Thanks in advance
>
>
>